An increasing number of people type 1 diabetes are participating in adventure activities at moderate or high altitude. Limited data suggests that diabetic individuals may be less 'successful'in these conditions. While rarely an issue at sea level, lung diffusing capacity can be a limiting factor for oxygen transport during exercise at increased altitude. In diabetics, this limitation may be exacerbated by impaired pulmonary diffusion which often goes unnoticed at sea level. The cause of diabetic pulmonary diffusion limitation is unclear, and may involve alveolar membrane diffusing capacity (DM) or pulmonary capillary blood volume (Vc). When exposed to the combination of exercise and increased altitude diabetic patients may experience arterial desaturation, which lowers functional capacity and may increase the prevalence of altitude illness. This study will use two parallel laboratories to measure diffusing capacity at low and moderate altitude (2150 meters) in type 1 diabetic and non-diabetic subjects who live at low altitude. By measuring multiple expired gases with a mass spectrometer (in both labs), we will partition out the influence of DM and Vc to determine which of these factors, if any, reduces pulmonary diffusion in diabetic subjects exercising at moderate altitude. An additional group of type 1 diabetic patients who live at moderate altitude will be studied to determine if diffusion limitation is attenuated or reversed by chronic moderate altitude exposure. Based on the findings of these studies, future research will determine whether aggressive glycemic control, which prevents the normal decline in pulmonary diffusing capacity in type 1 diabetics at sea level, will improve pulmonary diffusion and performance during acute moderate altitude exposure. PUBLIC HEALTH RELEVANCE: The diabetic lung is less capable of delivering oxygen from the air into the blood. This condition often goes unnoticed at low altitude where oxygen availability is high, however impaired lung function can have serious health consequences during physical exertion at increased altitude. The results of this study will determine whether impaired lung function limits people with diabetes from participating in high altitude activities, and provide a starting point for research designed to improve lung function.